1. Field of the Invention
The present invention relates to a discharge lamp (e.g. a metal halide lamp for a vehicle head lamp) driving device and method.
2. Description of the Related Art
Discharge lamps used for a vehicle head lamp are required to become stable as soon as turned on. In order to meet the requirement, a high pulse voltage typically is applied to the discharge lamp when it is turned on providing higher than regular power to raise lamp electrode temperature the until it becomes stable. Thereafter, the input power to the lamp is gradually reduced to regular operating power.
Usually, a time constant circuit composed of a capacitor and a resistor is used for gradually reducing initial turn-on power to regular operating power. If the regular power of the discharging lamp is 35 watts (W), the time constant of the time constant circuit is usually 6-8 seconds and the time required for the discharge lamp to become stable after it is turned on is about 30-40 seconds.
Therefore, such a long required turn-on time becomes a big problem when many drivers for discharge lamps are manufactured and tested.